Medical guidewires are used in numerous catheterization procedures as an aid to placement of a catheter and/or prosthesis at a selected site within a body lumen. The catheter is constructed to perform a particular procedure at that internal site. Among the more common uses of guidewire is in the catheterization of blood vessels for diagnostic or therapeutic purposes. In such a vascular catheterization procedure, the guidewire is inserted, usually percutaneously, into one of the patient's blood vessels and is manipulated and advanced through the branches of the vascular system to the target site. The catheter is then threaded over and advanced along the guidewire, with the guidewire serving to guide the catheter directly to the target site.
Guidewires may be extremely slender, in the order of 0.25 to 0.46 mm (0.010 to 0.018 inches) in diameter, but nevertheless must be capable of transmitting rotation from the guidewire proximal end to the distal end so that a clinician may controllably steer the guidewire through the branches of the patient's arteries and manipulate it to the target site in the intended body lumen. Additionally, the distal region of the guidewire must be sufficiently flexible to pass through sharply curved tortuous coronary anatomy, as well as to provide a sufficiently soft, distal tip that will not injure the artery. In addition, the guidewire must have sufficient column strength so that it can be pushed without buckling.
A guidewire configuration used in angioplasty is illustrated in U.S. Pat. No. 4,545,390 to Leary. Such a wire includes an elongate flexible shaft, typically formed from stainless steel, having a tapered distal region and a helical coil mounted to and about the tapered distal region. The generally tapering distal region of the shaft acts as a core for the coil and results in a guidewire having a distal region of increasing flexibility that is adapted to follow the contours of the vascular anatomy while still being capable of transmitting rotation from the proximal end of the guidewire to the distal end, so that the physician can controllably steer the guidewire through the patient's blood vessels.
Performance characteristics of the guidewire are affected by the construction of the guidewire distal tip. For example, in one type of tip construction, the tapering core wire extends fully through the helical coil to the distal tip of the coil and is attached directly to a smoothly rounded tip weld at the distal tip of the coil. Such a construction, referred to as a core-to-tip construction, typically results in a relatively stiff tip particularly suited for use through tight stenosis. In addition to a high degree of column strength, such a tip also displays excellent torsional characteristics.
In another type of tip construction, the tapered core wire terminates short of the tip weld. In such a construction, a very thin metallic ribbon may be attached between a distal end of the core wire and the smoothly rounded tip weld at the distal tip of the coil. The ribbon serves as a safety element to maintain the connection between the core wire and the distal tip weld in the event of coil breakage. It also serves as a shaping ribbon for receiving and retaining a bend or curve to maintain the guidewire distal segment in a bent configuration, as may be desirable when manipulating and steering the guidewire selectively into vessel side branches. Additionally, by terminating the core wire short of the tip weld, the segment of the helical coil between the distal end of the core wire and the tip weld is very flexible or “floppy.” The so-called floppy tip is desirable in situations where the vasculature is highly tortuous and in which the guidewire distal segment must be capable of conforming to and following the tortuous anatomy with minimal trauma to the blood vessel.
Floppy guidewire tips are used during implantation of prostheses within blood vessels or other similar organs of the living body. For example, rather than performing an open surgical procedure to implant a stent-graft that may be traumatic and invasive, stent grafts are preferably deployed through a less invasive intraluminal delivery. Prosthetic vascular stent grafts constructed of biocompatible materials, such as Dacron or expanded, porous polytetrafluoroethylene (PTFE) tubing, have been employed to replace or bypass damaged or occluded natural blood vessels. A lumen of the vasculature is accessed at a convenient and low trauma entry point, and a self-expanding compressed stent graft is routed through the vasculature to the site where the prosthesis is to be deployed. The catheter is then routed though a body lumen until the end of the catheter containing the stent graft is positioned at the intended treatment site, and the stent graft is deployed to radially self-expand so that at least a portion of it contacts and substantially conforms to a portion of the surrounding interior wall of the lumen, e.g., the blood vessel wall or anatomical conduit.
Grafting procedures are known for treating aneurysms. Aneurysms result from weak, thinned blood vessel walls that “balloon” or expand due to aging, disease and/or blood pressure in the vessel. Consequently, aneurysmal vessels have a potential to rupture, causing internal bleeding and potentially life threatening conditions. Grafts are often used to isolate aneurysms or other blood vessel abnormalities from normal blood pressure, reducing pressure on the weakened vessel wall and reducing the chance of vessel rupture. As such, a tubular endovascular graft may be placed within the aneurysmal blood vessel to create an artificial flow conduit through the aneurysm, thereby reducing if not nearly eliminating the exertion of blood pressure on the aneurysm.
While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries. Depending on the region of the aorta involved, the aneurysm may extend into areas having vessel bifurcations or segments of the aorta from which smaller “branch” arteries extend. Various types of aortic aneurysms may be classified on the basis of the region of aneurysmal involvement. For example, thoracic aortic aneurysms include aneurysms present in the ascending thoracic aorta, the aortic arch, and branch arteries that emanate therefrom, such as subclavian arteries, and also include aneurysms present in the descending thoracic aorta and branch arteries that emanate therefrom, such as thoracic intercostal arteries and/or the suprarenal abdominal aorta and branch arteries that emanate therefrom, such as superior mesenteric, celiac and/or intercostal arteries. Lastly, abdominal aortic aneurysms include aneurysms present in the aorta below the diaphragm, e.g., pararenal aorta and the branch arteries that emanate therefrom, such as the renal arteries.
Unfortunately, not all patients diagnosed with aortic aneurysms are presently considered to be candidates for endovascular grafting. This is largely due to the fact that most of the endovascular grafting systems of the prior art are not designed for use in regions of the aorta from which side branches extend. The deployment of endovascular grafts within regions of the aorta from which branch arteries extend presents additional technical challenges because, in those cases, the endovascular graft must be designed, implanted, and maintained in a manner which does not impair the flow of blood into the branch arteries.
To accommodate side branches, a main vessel stent graft having a fenestration or opening in a side wall thereof is often used. The fenestration is positioned to align with or at least be in the vicinity of the ostium of the branch vessel after deployment. In use, the proximal end of the graft having one or more side openings is securely anchored in place, and the fenestrations or openings are configured and deployed to avoid blocking or restricting blood flow into the side branches. Fenestrations alone do not form discrete conduit(s) through which blood is channeled into each side branch artery. As a result, the edges of the graft surrounding the fenestrations are prone to: i) the leakage of blood into the space between the outer surface of the aortic graft and the surrounding aortic wall; or ii) post-implantation migration or movement of the stent graft causing misalignment of the fenestration(s) and the branch artery(ies), which may result in impaired flow into the branch artery(ies).
In some cases, another stent graft, often referred to as a branch prosthesis, may then be deployed through the fenestration into the branch vessel to provide a conduit for blood flow to the branch vessel. The branch prosthesis is preferably sealingly connected to the main graft in situ to prevent undesired leakage.
Delivery of multiple stent grafts in a single procedure may involve multiple guidewires and/or additional procedural steps to manipulate the guidewire(s) and catheter(s) involved in placement thereof. There remains a need in the art for improvements for implantation branch prostheses for improving flow into the corresponding branch vessels. Embodiments hereof relate to a guidewire having floppy tips at both ends thereof to assist in the placement of a branch prosthesis.